Spark plug and method of making the same



O. C. ROHDE July 31,1934.

2 Sheets-Sheet 1 Filed Jan. 14, 1933 EQ======== I .v

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July 31, 1934. o. c. ROHDE SPARK PLUG AND METHOD OF MAKING THE SAMEFiled Jan. 14, 1933 2 Sheets-Sheet 2 Patented July 31, 1934 UNITEDSTATESPATENT OFFICE SPARK PLUG AND METHOD OF MAKING THE SAME Otto C.Rohde, Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo,Ohio, a corporation of Delaware Application January 14, 1933, Serial No.651,781

13 Claims. (Cl. 29-155.51)

This invention relates to a spark plug and a and out, this finish havingsome insulating propmethod of makingthe same. More particularly erties.The finish may be removed from the it relates to the formation-of agas-tight joint inner end of the counter bore in bushing 12 between themica insulation of the spark plug where it is contacted by beveled end22 of sleeve and the electrode on one side and the shell on 21, and fromthe shoulder.immediately opposite 60 the other side. Details and minorobjects of this point. the invention will appear as the description pro-With the parts thus assembled, they are placed ceeds. in the deviceshown in Figs. 2' and 4. This com- Inthe accompanying drawings forming apart prises an abutment member 30 supported by a of this specification,Fig. 1 is a sectional view of strong spring 31 upon a support 32. Rods33 85 an initial assembly in making one form of a extend upward fromsupport 32 and have fasspark plug embodying my invention; tened to theirupper end a cross piece 34 which Fig. 2 is a view of assembled mechanismfor has therein a socket 35 adapted to receive bushperforming the nextstep in the making ofthe ing 12. Below socket 35 there is an opening 36plug after that shown in Fig. 1; to receive the insulation 17. The upperend of 70 Fig. 3 is a longitudinal section of a spark plug abutment hasa socket 3'7 adapted to receive in the stage after it has been treatedby .the the lower end 16 of the electrode and surroundmechanism in Fig.2; ing insulation. Bushing 12 is held in socket Fig. 4 is an enlargedsection of the plug and y C mp g members 3 fas n d n place by 20immediately associated mechanism shown in screws 39. Fig. 2; A plungerhead 40 has an opening 41 therein Fig. 5 is a longitudinal section of acompleted to receive the electrode 14 and sleeve 15. The plug formed inaccordance with Figs. 1 to 4'. pp r D t On Of t s pening is e ed at 42The completed spark plug shown in Fig. 5 ei a p er S e 43 which has in t25 will be described first. In this view there is lower end a socket "44to receive the upper end shown the usual shell 10 having the screwthreads of electrod 4- Head 0 i e in j s D 11 adapted to be screwed intothe cylinder wall eitien up member 43 by a Screw 45 other of an internalcombustion engine. Within the ea s- A in 6 is cla ped about ea top ofthe shell there is threaded a bushing 12 means of a member 47. Y

30 seated upon a gasket 13. The central electrode Cross-head 34 isinsulated from other portions 14 has wound about its central portionmica of the mechanism and abutment 30 is preferably sheets 15 forming aninsulating sleeve; Beof non-conducting materiaL Cross-head 34 may tweenthe lower end 16 of the electrode and the be connected to a source ofelectricity by a terlower end of bushing 12 there is insulation minal at48, while another terminal is attached 35 formed by mica discs 1'? whilea similar series at 45. Thereupon with the parts in position as of micadiscs 18 is provided above the bushing shown in Fig. 4, electric currentpasses from and below the attachment member 19, which has cross-head 34t r bushing 12 i t lower a groove therein 20 for reception-ofa'terminal. end otfiller sleeve 21 and thence through plunger In themaking of the plug, the sleeve 15 is head 40. It will be understood thatspring 31 is 4o first wound upon electrode 14 and then mica suflicientlystrong to-insure proper compression discs 17 are placed in position.Thereafter bushof insulation 1'7 so that the bushing l2 is held in ing12 is placed around sleeve 15 above the discs properaelation toelectrode 14 and sleeve 15.

17 and a filler sleeve 21 is inserted between the Suflicient'current isemployed to meltth lower bushing and sleeve 15. In the form shown,filler end of the filler sleeve, first at its lower beveled 45 sleeve 21has a somewhat reduced lower end 22 end, then progressively valong thethin portion and a slightly thickened upper end 23 which is to shoulder26, then along the thicker portion to designed to" just fit within theupper bore 24 of upper end 23. Enough pressure is exerted on the bushing12. Below the upper end, the bore of upper end of filler sleeve 21toinsure the pressing bushing 12 is .enlarged as at 25. In the form downof its upper end as its lower end melts, and

50 shown, sleeve 21 isthinner above beveledend he curr nt isre that pperend23 re- 22 to shoulder 26 than thereabove to upper end m s hards dring is p e down 23. A low-manganese steel containing one or preferablyun il i is flu wi h Slightly l w two per cent manganese, for example,issuitable the top of he surreuhding'bushing. and forces material forthe sleeve. The steel bushing is the molten metal against thebushing'and mica.-

55 preferably given the usual black finish, inside Pressure is continuedwhile the metal sets.

The ring 23 forms a close fit with the top of the surrounding bushing,but preferably does not make good electric contact therewith during itsinsertion therein, as a good electric contact at this point tends toshunt the circuit around the lower part of the sleeve that isbeingprogressively melted. A very slight clearance, especially when aided bya black finish or similar slight coat, is sufiicient to preventdetrimental shunting.

After the pressing operation, the cooling of the heated metal aboutsleeve 15 further compresses that sleeve so that a thoroughly gastightjoint is produced at 50, (see Fig. 3). Since the metal of filler sleeve21 is seated in the bushing while molten, the fit is so close as to begastight under ordinary circumstances but, if desired, there is a weldedunion of the reduced lower end 22 of sleeve 21 with the bushing, asindicated at 51 on Fig. 3. This welded union is not ordinarily necessaryto make a gas-tight joint, but may be provided, if desired, for purposesof safety.

Upper ring 23 fits closely around sleeve 15, but

' is not shrunk thereon like the molten metal below, and consequentlythere is no sharp upper shoulder cutting into the mica. Likewise, thebevel 22 at the bottom not only aids in localizing the initial heat soas to start melting at that point, but also results in less pressure onthe mica at this point, so that the inner surface of the filler sleeveis somewhat convex in the finished plug, as shown-in Fig. 3, andprovides compression over a considerable length of the mica sleevewithout any sharp shoulder at any point that is likely to break orinjure the mica.

Since the metal is molten while being fitted into the counter bore ofthe bushing, it is pressed in every direction by the applied pressure,and conforms exactly to any irregularities in the contbur of the space,even such-slight irregularities as result from the beginning andterminations of the lamina of mica making up sleeve 15. The pressureexerted by ring 23 is sufilcient to insure this accurate fit, but neednot approach that necessary to deform solid metal. The slight expansionof the steel during solidification may assist in the close fit which itis found to have within the shell even after cooling to the 'temperatureof the shell.

After the parts are thus assembled, as shown in Fig. 3,the insulatingmembers 18 are placed in position after which a washer 52 is placedthereon and upper terminal member 19 is pressed down upon insulatingwashers. The upper end of the bore in member 19 is flared at 53 and thetop of the electrode is upset at 54 so as to rivet the parts inassembled relation. The bushing 12 is then screwed into sleeve 10 to.form the completed plug shown in Fig. 5.

By the above described arrangement it will be seen that there isprovided a permanent gastight joint between the insulating member andthe surrounding metallic member bywhich the spark plug is mounted.

While one construction has been shown in considerable detail, it will.be understood thatchanges in the details of the method and plug may bema e within the scope of the appended claims, wher in the term shell isintended to ing a, shell onto a non-vitreous insulating tube surroundingan electrode which consists in exerting pressure upon molten metal inthe space between the shell and tube, and maintaining the pressure untilthe metal solidifies, the solidified metal as it cools shrinking ontothe tube.

2. In making a spark plug, the method of sealing a shell onto anon-vitreous insulating sleeve surrounding an electrode, which consistsin exerting pressure upon molten metal in the space between the shelland tube, and maintaining the pressure while the metal sets ininterlocking engagement with the shell and in intimate contact with thetube, the solidified metal as it cools shrinking onto the tube.

3. In making a spark plug, the method which consists in winding thinmica sheets about an electrode and thereby forming an insulating tube,surrounding the tube with a shell, exerting pressure upon molten metalinthe space between the shell and tube, and maintaining the pressurewhile the metal sets in intimate contact with the shell and tube, thesolidified metal as it cools shrinking onto the tube, thereby pressingthe tube against the electrode.

4. In making a spark plug, the method which consists in winding thinsheets of mica around an electrode to form an insulating tube,surrounding the tube with a shell having an undercut counter bore,exerting pressure upon molten metal in the counter bore and maintainingthe pressure while the molten metal solidifies in intimate contact withthe tube and with the undercut portion of the counter bore, thesolidified metal as it cools shrinking onto the tube.

5. In making a spark plug, the method of sealing a shell onto anonvitreous insulating tube surrounding an electrode, which consists inintroducing between the shell and tube a metal sleeve while melting thesleeve progressively, beginning at its inner end, and pressing themolten metal melted end into the space between the shell and tube andthereby forcing the molten metal into close contact with the shell andtube, and solidifying the molten metal .,while it is in such closecontact, the metal as it cools shrinking onto the tube. v

7. In making a spark plug, the method which consists inwinding thin micasheets about an electrode and thereby forming an insulating tube,

surrounding the tube with a shell having a grooved counter bore aroundthe tube, inserting a metal sleeve into said counter bore, melting theinner end of the sleeve progressively while it is being inserted, andcontinuing to press the unmelt ed outer end of thesleeve into thecounter bore while allowing the molten metal to solidify in interlockingengagementwith said groove and in intimate contact with said tube, thesolidified metal shrinking onto the tube as it cools, therebycompressing the tube against the electrode.

8. In making a spark plug, the method which I consists in placing ametal shell around a nonvitreous insulating tube surrounding anelectrode, introducing a steel sleeve into the space between the shelland tube, forcing the inner end of the sleeve into contact with theshell, passing an electric current through a portion of the shell andthrough the sleeve and thereby melting the sleeve progressively from itsinner end towards its outer end, but leaving the outer end unmelted,pressing the unmelted outer end of the sleeve into said space andthereby bringing the molten metal into intimate contact with the shelland tube, and solidifying and cooling the steel and thereby sealing theshell to the tube and compressing the tube onto the electrode.

9; In making a spark plug, the method which consists in placing a shellaround a non-vitreous insulating tube surrounding an electrode,introducing a manganese steel sleeve into the space between the shelland tube, passing an electric current through the sleeve to melt theinner end thereof, and pressing the unmolten outer end of the sleeveagainst the molten metal and solidifying the molten metal underpressure, the

solidified metal as it cools shrinking onto the tube.

10. In making a spark plug, the method which consists in winding thinsheets of mica around an electrode to form an insulating tube,surrounding the tube with a metal shell having a counter bore aflordinga space between the shell and tube, inserting a manganese steel sleeveinto the said space, making an electric contact between the shell andinner end of the sleeve and passing an electric current through theshell and sleeve through said contact and thereby melting the inner endof the sleeve, and pressing the molten metal into said space while itsolidifies, the solidified metal shrinking onto the tube by cooling.

11. A spark plug comprising a central electrode, a non-vitreousinsulating tube surroundin the electrode, a shell surrounding thesleeve, and a metal seal between the shell and tube, said seal beingfitted in place while molten and under pressure and thereby exactlyfitting all irregularities in contour of the interior of the shell andexterior of the tube, and shrunk onto the tube and pressing the tubeinto sealing contact with the electrode.

12. A spark plug comprising a central electrode, a mica tube around theelectrode, a shell around the tube, and a steel seal, pressed into placewhile molten, between the shell and tube, and thereby fitting exactlythe contour of the interior of the shell and exterior of the tube andbeing shrunk onto the tube arid pressing it into sealing contact withthe electrode. 13. In making a spark plug, the method of sealing a shellonto a non-vitreous insulating tube surtoundingan electrode, whichconsists in exerting pressure upon molten metal in the space between theshell and tube andmaintaining the pressure until the metal solidifies,said metal when cooling having its degree of shrinkage gradually reducedat its outer end to avoid a sharp shoulder in impingement with theinsulating tube.

-' OTIO C. ROHDE.

